1. Field of the Invention
The present invention relates to a multi-optical-axis photoswitch incorporating a light emitting unit and a light receiving unit between which a multiplicity of optical axes exist which are realized by pairs of light emitting devices and light receiving devices in a detection area thereof, and more particularly to a state display method for displaying a light shielding state or the like of the multi-optical-axis photoswitch and a multi-optical-axis photoswitch adapted to the method.
2. Description of the Related Art
The multi-optical-axis photoswitch is a switch having a plurality of optical axes formed by pairs of light emitting devices of a light emitting unit and light receiving devices of a light receiving unit and arranged to be operated when any one of the optical axes is shielded by an object. Hitherto, the multi-optical-axis photoswitch has been known as an xe2x80x9coptical area sensorxe2x80x9d which is capable of detecting existence of an object in a wide detection area. The multi-optical-axis photoswitch is used to improve safety of an operator of a machine tool, a punching machine, a pressing machine, a controller, a molding machine, an automatic controller, a winding machine, a robot, a casting machine or the like. The foregoing multi-optical-axis photoswitch is disposed in a dangerous region for a pressing machine or the like to form a detection area and to detect shielding of an optical axis which is caused when a portion of the body of an operator, for example, the finger or the hand of the operator, enters the detection area. Thus, the operation of the machine is interrupted or an alarm is issued to protect the operator.
Further, the multi-optical-axis photoswitches are disposed along automatic manufacturing lines in a plant to detect existence of moving articles. Thus, the multi-optical-axis photoswitches are employed as sensors in an automatic control system with which a next step is started if an article is detected.
A multi-optical-axis photoswitch of the foregoing type, as shown in FIG. 8, incorporates a light emitting unit 2 constituted by disposing a plurality of (eight in the structure shown in FIG. 8) light emitting devices 21, such as light emitting diodes (LED) which emit infrared rays, at predetermined pitches. Moreover, the multi-optical-axis photoswitch incorporates a light receiving unit 3 constituted by disposing light receiving devices 31, such as photodiodes, at predetermined pitches to correspond to the light emitting devices 21 in order to receive optical axes 5 which are infrared beams emitted from the light emitting devices 21 of the light emitting unit 2. The light emitting unit 2 is disposed at one end of a detection area which is provided for a pressing machine or the like and which must be protected. On the other hand, the light receiving unit 3 is disposed at the other end of the detection area such that the light emitting unit 2 and the light receiving unit 3 are disposed opposite to each other. Light beams are emitted and received between the pairs of the light emitting devices and the light receiving devices of the light emitting unit 2 and the light receiving unit 3. Thus, whether or not each light beam is shielded is detected. The light emitting unit 2 and the light receiving unit 3 are connected to each other through a signal line 8.
The light emitting unit 2 is controlled by a light-emitting-unit control circuit so that the light emitting devices 21 of the light emitting unit 2 sequentially and cyclically emit light from one end of the light emitting devices 21 to the other end of the same (for example, in an upward direction from the lowest device). In synchronization with the light receiving devices 31 of the light receiving unit 3 corresponding to the light emitting devices 21, only the corresponding light receiving device 31 is enabled to receive light and the other light receiving devices 31 are made to be impossible to receive light. The reason why only one light receiving device 31 is always enabled to receive light lies in that light emitted from a light emitting device 21 is not always received by only a corresponding light receiving device 31. Therefore, a case can be considered that relatively intense light is made incident on also light receiving devices 31 adjacent to the correspond light receiving device 31. That is, the structure is formed such that light receipt signals from all of the light receiving devices 31 are collectively supplied to one binarizing circuit. Therefore, even if one optical axis is shielded because of introduction of an object, light made incident on the adjacent light receiving devices 31 causes the overall intensity level of light to exceed a threshold value. Thus, an incorrect determination is made that the state is a state in which light can be received. Thus, introduction of an object cannot accurately be detected.
Only one optical axis is cyclically and always made to be effective as described above to continue detection. If an object or fingers or hand of a human being is introduced into the detection area, an optical axis 5 at that position is shielded. Thus, the light receiving device 31 cannot receive light. Therefore, an alarm is issued or the operation of the machine is interrupted to improve safety.
FIG. 9 is a block diagram showing a sensor portion of the multi-optical-axis photoswitch 1 shown in FIG. 8. The multi-optical-axis photoswitch 1 is composed of the light emitting unit 2 and the light receiving unit 3.
The light emitting unit 2 incorporates N light emitting devices 21 (211, 212 to 21N) disposed at required pitches, for example 40 mm and comprising light emitting diodes or the like, N being a required number. Moreover, the light emitting unit 2 incorporates N light emitting circuits 22 (221, 222 to 22N) for operating the light emitting devices 21; a light-emitting-device switching circuit 23 to scan the N light emitting circuits 22 in a time division manner; a light-emitting-unit control circuit 24; and a display unit 6 for displaying a state of the multi-optical-axis photoswitch 1.
The light-emitting-unit control circuit 24 employs a gate array in this case to perform control. As a matter of course, another control device, for example, a CPU, may be employed in place of the gate array.
If the display unit 6 is composed of one display lamp which displays, for example, red and green light, green light is displayed when all of the optical axes are ensured. In the other cases, red light is displayed. If a monochrome display lamp is employed, the lamp is turned on when all of the optical axes are ensured. In the other cases, the lamp is turned off.
The light receiving unit 3 incorporates N light receiving devices 31 (311, 312 to 31N) disposed at the same pitch as that in the light emitting unit and comprising phototransistors or the like, N being a required number. Moreover, the light receiving unit 3 incorporates N light receiving circuits 32 (321, 322 to 32N) for I-V converting light receipt signal from each of the light receiving devices 31; and a light-receiving-device switching circuit 33 for scanning the N light receiving circuits 32 in a time division manner in synchronization with the light emitting devices 21 forming pairs with the N light receiving circuits 32. In addition, the light receiving unit 3 incorporates an amplifying circuit 361 for collectively amplifying light receipt signals from the light receiving circuits 32; and a binarizing circuit 362 for converting the amplified signals into 1 or 0 with respect to a predetermined threshold value. Moreover, the light receiving unit 3 incorporates a detection circuit 363 for determining a state of incident light by using the binarized signal; a light-receiving-unit control circuit 34 for controlling the light receiving unit 3; and an output circuit 35 for interrupting the operation of the pressing machine or the like.
The light-receiving-unit control circuit 34 employs a gate array similarly to the light-emitting-unit control circuit 24. As a matter of course, another control device, for example, a CPU, may be employed in place of the gate array.
The structure shown in FIG. 9 is formed such that the display unit is provided for the light receiving unit 3 and the same is omitted from the light emitting unit 2. Depending on a state of use, a display unit may be provided for the light emitting unit 2 in place of the display unit 6 provided for the light receiving unit 3.
The signal line 8 is provided for supplying a synchronizing signal for synchronization between the light emitting unit 2 and the light receiving unit 3 from the light receiving unit 3 to the light emitting unit 2.
Moreover, a light emission/receipt monitoring circuit (not shown) is provided for each of the light emitting unit 2 and the light receiving unit 3. Thus, whether or not each of the light emitting devices and light receiving devices is being operated normally is always monitored. When an abnormal condition, such as a breakdown of the device, occurs, an alarm can quickly be issued to the operator.
The state of the operation of a multi-optical-axis photoswitch of the foregoing type has been displayed by the following three methods:
(1) A first method of displaying an operation state uses one display unit 6, as shown in FIG. 10. When all of the optical axes are ensured, the display unit emits green light. In the other cases, that is, in cases where one or more optical axes are shielded, the display unit 6 is turned off (or red light is emitted).
(2) A second method of displaying an operation state uses a plurality of display units 6 as shown in FIG. 11. That is, one display unit is disposed adjacently to each of the light emitting devices 21 so as to display the operation state.
(3) A third method of displaying an operation state has a structure that one display unit is blinked to display the operation state. That is, the blinking rate is changed to display a ratio of the number of optical axes through which light passes. In this method,
1) If light passes through one optical axis, the display unit is blinked at intervals of {fraction (3/10)} second.
2) If light passes through four optical axes, the display unit is blinked at intervals of {fraction (1/10)} second.
3) If light passes through seven optical axes, the display unit is blinked at intervals of {fraction (1/20)} second.
However, the above-mentioned conventional examples have the following problems:
(1) In the case of the first method, adjustment of the optical axis from the light emitting unit to the light receiving unit cannot conveniently be performed. That is, the display unit continues the state in which it is turned off (or emits red light) if all of the optical axes are not ensured. Therefore, even if the light emitting unit (or the light receiving unit) is moved vertically and horizontally with respect to a plane made by the light receiving unit (or the light emitting unit) during the optical axis adjustment, the display unit continues the state in which it is turned on (or emits red light) unless all of the optical axes are ensured. As a result, there arises a problem that a correct direction of movement cannot be determined.
(2) In the case of the second method, the inconsistent optical axis can immediately be detected. However, all of the display units must be observed from one end display unit to the other end display unit of the light receiving unit (or the light emitting unit) to detect whether or not the number of optical axes through which light passes has increased when the light emitting unit (or the light receiving unit) is moved. Therefore, satisfactory visibility cannot be obtained. What is worse, each light axis must be provided with the display unit. Therefore, the overall size cannot be reduced, causing the cost to be enlarged. Therefore, there arises a problem that the number of elements other than original elements increases.
(3) In the case of the third method, adjustment of the optical axes cannot conveniently be performed. This method enables only the ratio of optical axes through which light passes to be detected in accordance with an absolute blinking rate. Information about a direction in which the optical axis must be moved cannot be obtained. That is, the direction into which the movement must be performed is detected in accordance with change in the blinking rate occurring when movement in which direction has been performed. To detect change in the blinking rate, the blinking rate must be counted for a predetermined time. Therefore, the direction into which the movement must be performed cannot instantaneously be detected. What is worse, thorough knowledge of the blinking rate with respect to the ratio of the number of the optical axes through which light passes is required to adjust the optical axes. Therefore, a beginner cannot easily perform the adjustment.
Accordingly, the present invention is arranged to solve the above-mentioned problems by displaying a state in the form of a bar graph. According to the present invention, adjustment of optical axes can be performed by performing movement in a direction in which the value of the bar graph increases. Thus, adjustment of the optical axes can easily be performed. As a result, a beginner is able to easily adjust the optical axes. Since display lamps are concentrically disposed, the bar graph can immediately be recognized. Since the necessity required for the conventional structure (2) to observe the overall area of the light emitting unit can be eliminated, the visibility of the display of the state can be improved. An object of the present invention is to provide such a display method and a multi-optical-axis photoswitch.
To achieve the above-mentioned object, according to an aspect of the present invention, there is provided a state displaying method for displaying a state of a multi-optical-axis photoswitch which incorporates a light emitting unit and a light receiving unit between which a multiplicity of optical axes exist which are realized by pairs of emitted light and received light, the method comprising the steps of: calculating a ratio of the number of optical axes in which a quantity of received light has exceeded a predetermined threshold value with respect to the number of all of the optical axes; and causing a plurality of display lamps disposed concentrically to display the calculated ratio.
According to another aspect of the present invention, there is provided a multi-optical-axis photoswitch incorporating a light emitting unit and a light receiving unit between which a multiplicity of optical axes exist which are realized by pairs of emitted light and received light, the photoswitch comprising: a counter for counting the number of optical axes in which a quantity of received light has exceeded a predetermined threshold value; displaying means including a plurality of display lamps disposed concentrically; calculating means for calculating a ratio of the number of optical axes counted by the counter with respect to the number of all of the optical axes; and display control means for controlling the plural display lamps to display a result of a calculation performed by the calculating means as a bar graph.